A typical disc drive includes one or more discs having data surfaces for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor that causes the discs to spin and the data surfaces of the discs to pass under transducers, which write information to and read information from the data surfaces of the discs.
Areal density is a measure of data bits per unit of surface area of the medium. The areal density is a function of the number of tracks-per-inch (TPI) along the radius of the disc and the number of bits-per-inch (BPI) along the tracks. The bits-per-inch value for a particular track is a function of the data transfer rate, the data encoding rate, the radial position of the track, and the angular speed of the medium. In most disc drives, the TPI and BPI for the disc drive are set based on a desired storage capacity for the drive and the nominal performance characteristics of the transducers. Under some prior art disc drives, different radial zones on the drive were assigned different TPI values to take advantage of different performance characteristics of the transducer at different radial positions along the disc.
Once the TPI and BPI values are designated for a drive, the manufacturer of the transducers attempts to build transducers that can meet the designated TPI and BPI values. Due to variations in the manufacturing process, some of the transducing heads have less than ideal geometry properties, unfit for the TPI requirements. Geometry problems are a major factor impacting transducers' write and read performance.
In the past, heads that could not satisfy the TPI or BPI requirement were discarded. Recently, attempts have been made to overcome the shortcomings of some heads by increasing the storage capacity associated with other heads in the drive to compensate for the lost storage capacity of the under-performing heads. However, this requires the TPI and/or BPI of a number of heads to be changed simply because one head has not met specifications. This is less than desirable. Thus, a system is needed that will result in fewer transducing heads being discarded but at the same time will require as few changes as possible to the capacity design point of the disc drive.
Embodiments of the present invention address these and other problems, and offer other advantages over the prior art.